Some corbiculids (bivalve clams in the genus Corbicula) are invasive, having spread nearly worldwide and are thought to impact native unionid mussels. To determine the density and distributional associations of invasive corbiculids co‐occurring with native unionids, corbiculid clam and unionid mussel surveys were conducted at 122 sites in the Kalamazoo River catchment, Michigan, U.S.A. Unionid densities ranged from 0 to 97 (x̅ = 7.45 ± 15.38 SD) live unionids found per person hour while corbiculid densities varied from 0 to 0.24 (0.012 ± 0.037) g/cm3. Corbiculid distributions were clumped (Moran's I test: Index = 0.281, Z = 2.228, p = 0.026) and highest along the main branch of the river. Unionid distributions, both individual species and at family level, were found to be randomly distributed throughout the catchment (Moran's I test: Index = 0.343 to −0.022, Z = 1.913 to −0.118, p value = 0.056 to 0.970). Overall, unionid species richness, as well as the distribution of 13 unionid species, were negatively associated with corbiculid density. Although corbiculids can inhabit the same river reaches with unionids, unionid species richness and densities may be negatively influenced by the presence of corbiculids. Although many species of unionids were negatively associated with corbiculid density, our research showed that they can co‐exist in the same river reaches. Overall, unionids were positively correlated with corbiculids throughout the catchment, probably because the two groups have similar habitat requirements. It is therefore important to consider unionids and corbiculids concurrently in conservation planning and the management of invasive corbiculids.

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